This invention relates to a method of manufacturing an in-the-ear heating aid which is inserted into an ear canal of a person against or near a tympanic membrane, which method employs a mould of the ear canal of the person's ear. The mould is used for making a moulding die for the manufacture of a heating-aid housing. An auxiliary tool comprising a flexible tube having a flange at one end is inserted into the ear canal with said end in order to form the mould, after which a curable material is introduced into the ear canal and, after the material has cured, the material with the tube and the flange is removed from the ear canal.
The external shape of such in-the-ear hearing aids should correspond to the shape of the ear canal. In order to determine the shape of the ear canal moulds are made of the ear canal of a person. These moulds define the dimensions of hearing-aid housings to be manufactured.
A method of making an ear mould is known from U.S. Pat. No. 3,440,314. The ear mould described therein is used for holding a hearing-aid receiver. In the prior-art method the flange closes the tube at one end and the tube is inserted into the ear canal over a part of the length of the ear canal. Subsequently, the tube is filled with a liquid metal which after solidifying keeps the tube in position. After removal of the mould the solidified material and the flange are removed and the tube serves as the acoustic duct. Since this receiver is not fitted in the ear canal the ear mould is formed over only a part of the ear canal.
In modern hearing aids the heating aid is situated near or against the tympanic membrane of the ear. If such a hearing aid is to be custom-made, a mould up to the tympanic membrane is required. If the prior art method would be used for making an ear mould up to the tympanic membrane, a partial vacuum would be produced between the tympanic membrane and the ear mould during removal of the mould, so that removal would be painful or might even cause damage to the tympanic membrane. Ear moulds up to only half the length of the ear canal do not present this problem because the partial vacuum which can be produced is much smaller owing to the large volume of air in the rear part of the ear canal. Moreover, when such ear moulds are removed the ear canal is deformed at the location of the mould, for example, by pulling at the auricle, thereby admitting air past the ear mould to the space between the ear mould and the tympanic membrane. This is not possible in the case of ear moulds which extend up to the tympanic membrane because starting from the tympanic membrane the ear canal is surrounded with non-deformable bony tissue over some distance, so that this part of the ear canal cannot deform.